1. Field of the Invention
The present invention relates to metallic honeycomb carrier bodies, and, more particularly, to such metallic honeycomb carrier bodies for use as catalytic converters in vehicular engines to control exhaust emissions, and to methods for the manufacture of such carrier bodies and converters.
2. Description of the Related Art
Metallic honeycomb carrier bodies for catalytic converters have been formed conventionally by arranging corrugated thin metal foil sheets in a core body to provide fluid passageways or "cells" extending between opposite ends of the body. The body thus formed is secured within a jacket tube by soldering, brazing or welding to provide structural support for the foil sheets.
Most typically, the fluid passageways have been formed by alternating layers of corrugated and relatively flat foil sheets so that to the extent the foil sheets are in full contact with each other, the individual passageways are self contained or represent closed cells in cross section. The flat sheets additionally function to separate the corrugated sheets, which otherwise would nest one within the other without open space for the passage of fluid.
Open honeycomb core structures have been formed entirely of superimposed corrugated sheets in which the pattern of corrugations prevents nesting of adjacent sheets. For example, the metallic foil sheets may be formed with chevron-shaped corrugations in a "herringbone" pattern so that when adjacent sheets are reversed end for end, the corrugations on one sheet cross those of the other sheet at points of contact to prevent nesting. The resulting pattern of passageways across the widths of the sheets extend in crossing zig-zag paths and are in the nature of trough-like channels in fluid communication with each other because the tops of the channels are open except at the points of crossing by the corrugations of an adjacent sheet.
A problem with the herringbone pattern of corrugations is a weakness at the points where the corrugations change directions. In particular, under heat and physical stress, these points of weakness tend to fracture with use, especially under conditions peculiar to automotive catalylitic converters. In addition the zig-zag paths of the flow passages in a herringbone pattern tend to create an unwanted high pressure drop under fluid flow velocities.
An open honeycomb core structure is also obtained by superimposing adjacent corrugated sheets in which the corrugations extend along straight lines skewed across the widths of the sheets at oblique angles to the lengths of the sheets. By reversing any two such sheets end for end, a crossing pattern of corrugations and passageways is formed across the widths of the sheets. Although the passageways are again in the nature of interconnected troughs, they extend linearly across the widths of the sheets, albeit in crossing angular paths, and present less obstruction to fluid flow than the zig-zag paths of the chevron pattern of corrugations.
Although the skewed crossing pattern has been recognized as useful for honeycomb carrier bodies for catalytic converters, there has been very little, if any, practical application of this pattern to metallic catalytic converters for use by the automotive industry, which requires survival of very severe tests known as the Hot Shake Test, the Hot Cycling Test, combinations of these tests, cold vibration testing, water quench testing, and impact testing.
The Hot Shake test involves oscillating (50 to 200 Hertz and 28 to 80 G inertial loading) the device in a vertical, radial or angular attitude at a high temperature (between 800 and 1050degrees C.; 1472 to 1922 degrees F., respectively) with exhaust gas from a gas burner or a running internal combustion engine simultaneously passing through the device. If the device telescopes, or displays separation or folding over of the leading or upstream edges of the foil leaves, or shows other mechanical deformation or breakage up to a predetermined time, e.g., 5 to 200 hours, the device is said to fail the test.
The Hot Cycling Test is run with exhaust flowing at 800 to 1050 degrees C.; (1472 to 1922 degrees F.) and cycled to 120 to 200 degrees C. once every 13 to 20 minutes for up to 300 hours. Telescoping or separation of the leading edges of the thin metal foil strips, or mechanical deformation, cracking or breakage is considered a failure.
Also, the Hot Shake Test and the Hot Cycling Test are sometimes combined, that is, the two tests are conducted simultaneously or superimposed one on the other.
To survive these automotive industry tests, it is important that the core body of the honeycomb carrier is strongly secured at its periphery to the interior of the supporting jacket tube. In using foil sheets with a skewed pattern of corrugations, for example, and to accommodate different jacket tube cross-sectional shapes, the core body is most efficiently formed by reverse folding a continuous strip of corrugated sheet material in programed accordion fashion so that lines at outside folds generate a body core periphery complementing the interior of the jacket tube.
Because of inaccuracies inherent in folding the corrugated strip, it is not possible, using presently known folding equipment, for every outside fold to lie with precise uniformity at the core body periphery intended to complement the jacket tube interior. Some of the folds will lie slightly within and others will lie slightly outside the intended core body periphery. As a result, all outside folds, which represent the ends of the working sheets in the carrier core body, cannot be secured to the jacket interior with equal strength, using known soldering or brazing techniques. More significantly, many of the folds may remain fully unsecured to the jacket tube interior, thus leading to failure of the carrier body during conduct of the described testing.
From the foregoing, it will be appreciated that catalytic converter bodies and their method of manufacture have received considerable attention, particularly by the automotive industry, are complex in design and manufacture, and are in need of improvement.